2007 R&D 100 Award Entry Form Mode-Filtered Fiber Amplifier · 2020. 9. 4. · 2007 R&D 100 Award Entry Form Mode-Filtered Fiber Amplifier Dahv A.V. Kliner Distinguished Member of

2007 R&D 100 Award Entry Form Mode-Filtered Fiber Amplifier

�


�

Submitting Organization Dahv A.V. Kliner

Sandia National Laboratories

P.O. Box 969, Mail Stop 9056

Livermore, CA 94551, USA

925-294-2821 (phone)

925-294-2595 (fax)

[email protected]

AFFIRMATION: I affirm that all information submitted as a part

of, or supplemental to, this entry is a fair and accurate represen-

tation of this product.

(Signature)_________________________________________

Naval Research Laboratory (NRL), Nufern Corporation, and

Liekki Corporation

Sandia and NRL are co-inventors of the Mode-Filtered Fiber

Amplifier technology described in this application; the

patent for this technology is held by the U.S. Government

and is currently administered by NRL. Liekki and Nufern are

licensees who produce commercial products using the

subject technology.

Rita Manak

Naval Research Laboratory

4555 Overlook Avenue SW

Washington, DC 20375-5320, USA

202-767-3083 (phone)

202-404-7920 (fax)

[email protected]

Joint Entry


�

Mike O’Connor

Nufern Corporation

7 Airport Park Road

East Granby, CT 06026, USA

866-466-0214 (phone)

866-844-0210 (fax)

[email protected]

Per Stenius

Liekki Corporation

Sorronrinne 9

Lohja, 08500, Finland

+358-19 357391 (phone)

+358-19 3573949 (fax)

[email protected]

Mode-Filtered Fiber Amplifier

The Mode-Filtered Fiber Amplifier is a breakthrough technology

that enables fabrication of practical, high-power, high-

beam-quality laser sources that are compact, rugged, and

extremely efficient.

The first commercial license for this technology was granted in

2005, and the first commercial products were offered by

co-applicants Nufern and Liekki in 2006.

Product Name

Product First Marketed or Available for Order

Brief Product Description


�

Dahv A.V. KlinerDistinguished Member of Technical StaffSandia National LaboratoriesP.O. Box 969, MS 9056Livermore, CA 94551, USA925-294-2821 (phone)925-294-2595 (fax)

[email protected]

Jeffrey P. KoplowPrincipal Member of Technical StaffSandia National LaboratoriesP.O. Box 969, MS 9056Livermore, CA 94551, USA925-294-2458 (phone)925-294-2595 (fax)

[email protected]

*Jeff Koplow was employed at the Naval Research Laboratory at the time of the Invention

Lew GoldbergLaser Technology Branch ChiefNight Vision LaboratoryAMSRD CER NV ST LT10221 Burbeck Rd.Fort Belvoir, VA 22060-5806, USA703-704-1366 (phone)

703-704-1352 (fax)

[email protected]

* Lew Goldberg was employed at the Naval Research Laboratory at the time of the Invention

David MachewirthDirector, Fiber Laser Engineering Nufern Corporation7 Airport Park RoadEast Granby, CT 06026, USA866-466-0214 (phone)866-844-0210 (fax)

[email protected]

Inventors or Prinicipal Developers


�

Mircea Hotoleanu

Fiber Product Development Manager

Liekki Corporation

Sorronrinne 9

Lohja, 08500, Finland

+358-19 357391 (phone)

+358-19 3573949 (fax)

[email protected]

Sandia National Laboratories and NRL do not sell commercial

fiber amplifiers; rather their government-owned technology is

licensed to commercial partners. Liekki and Nufern have

licensed the patent and manufacture a number of products

that employ the mode-filtering technology. These products

range from mode-filtered fiber coils (for incorporation into

lasers and amplifiers by other companies) to complete laser

systems. Liekki and Nufern also produce fibers whose design

is optimized for mode filtering; these fibers are sold to

manufacturers of lasers and laser-based instruments, as well

as to R&D organizations.

The patent related to this technology is U.S. 6,496,301: Helical

Fiber Amplifier, invented by Jeffrey P. Koplow, Dahv Kliner, and

Lew Goldberg, issued December 17, 2002 (see Appendix A for

an image of the first page).

Product Price

Patents or Patents Pending

Inventors or Prinicipal Developers


�

Product’s Primary Function Since their invention in 1963, fiber lasers have been recognized

as possessing extraordinary attributes that could revolutionize

the application of lasers to real-world problems by enabling

compact, rugged optical sources with high beam quality.

Fundamental limitations of previous fiber-based laser technolo-

gies, however, rendered impractical numerous high-power laser

applications. The Sandia/NRL Mode-Filtered Fiber Amplifier

enables dramatic power scaling of fiber lasers (by more than

100x), thereby addressing these long-standing limitations and

making real-world applications practical. In particular,

Mode-Filtered Fiber Amplifiers offer:

• High electrical efficiency (5x improvement over

conventional solid-state lasers);

• Low waste-heat generation and facile thermal

management;

• High optical gain;

• Broad wavelength coverage; and

• Diffraction-limited beam quality (explained below)

that is insensitive to environmental or operating

conditions, such as vibrations, thermal fluctuations,

and optical power level.

— all in a package that is an order-of-magnitude smaller than

traditional solid-state laser sources. As a result of this unique

combination of characteristics, the Sandia/NRL invention has

been licensed and commercialized by five companies, including

co-applicants Liekki Corporation and Nufern Corporation.


�

How Fiber Lasers WorkFigure 1a illustrates the basic components of a high-power

laser system. In the case of a fiber laser, the gain medium is an

optical fiber, consisting of a glass core (typically fused silica)

doped with a rare-earth element surrounded by a glass

cladding with a lower refractive index (Figure 1b). Typical

rare-earth dopants used in the core include ytterbium (Yb)

ions and erbium (Er) ions. The rare-earth ions are excited or

“pumped” by injecting light from an external pump source,

typically a laser diode, into the fiber; the pump light is absorbed

by the rare-earth ions. When the excited rare-earth ions drop

back to the ground state, they emit light in specific wavelength

bands; that is, the excited ions provide “optical gain.” Coherent

laser light is obtained either by seeding the fiber amplifier with

a low-power laser (in a “master oscillator – power amplifier”

configuration, as shown in Figure 1a) or by incorporating the

gain fiber into a laser cavity (i.e., by providing feedback at the

fiber ends using mirrors or fiber Bragg gratings – as illustrated

in Figure 12). Yb-doped silica fibers provide gain in the ~1000–

1200 nm region, and Er-doped silica fibers provide gain in the

~1500–1600 nm “eye-safe” region.

Product’s Primary FunctionFigure 1a: Key components of a high-power laser system.

Figure 1b: Fiber gain medium


�

The same functional description involving pump light, a gain

medium, and output light applies to any solid-state laser. Fiber

lasers represent an important step in the evolution of this class

of devices, providing the unique advantages listed above.

The characteristic of diffraction-limited beam quality is key to

understanding the significance of the Sandia/NRL mode-filtering

invention and requires additional explanation. The

theoretical limit for the spatial beam quality of a laser is known

as the “diffraction limit.” Diffraction-limited beams (also known

as “Gaussian” or “single-mode*” beams) provide the lowest

possible divergence and therefore the tightest possible focus.

These characteristics are crucial for delivering high intensities

(e.g., for materials processing) and small spot sizes (e.g., for

micro-drilling), as well as for projecting a laser beam over a

great distance with minimum spreading (e.g., for free-space

communication and remote sensing). A so-called “single-mode”

fiber supports only the “fundamental mode,” which is

diffraction limited; a single-mode fiber laser therefore produces

a diffraction-limited output beam. By contrast, conventional

multimode laser sources produce non-diffraction-limited out-

put beams that are unstable, irreproducible, undesirably struc-

tured, and excessively divergent. These concepts are made

more concrete in Figures 3 and 4, which show pictures of the

various fiber modes and examples of single-mode and multi-

mode beam quality.

How Mode-Filtered Fiber Amplifiers Work

The core of a single-mode fiber is relatively small (typically less

than 10 microns in diameter), which limits both the energy

storage and the power-handling capability of the fiber. Attempts

to increase power by increasing core diameter were met with

corresponding decreases in beam quality because larger-

diameter cores operate on multiple modes – a fatal disadvan-

tage in most applications. It was thus believed that fiber lasers

were limited to low-power operation by fundamental physical

properties of the fiber.

Product’s Primary Function

* “Modes” are the mathematical solutions to Maxwell’s Equations for light propagating in the fiber, and a single-mode fiber allows only one solution (the diffraction-limited fundamental mode). Multimode fibers (and multimode lasers in general) permit many modes, most of which are not diffraction-limited, with a consequent degradation in beam quality.


�

The Sandia/NRL Mode-Filtered Fiber Amplifier technology

enables dramatic power scaling (by at least two orders of

magnitude) of diffraction-limited fiber sources by allowing a

highly multimode fiber to operate stably on a single mode. A

key breakthrough was made in 2000, when Sandia/NRL

researchers demonstrated that bend loss in a coiled fiber can

act as a form of distributed spatial filtering to suppress all but

the fundamental mode of a highly multimode (large core

diameter) fiber amplifier – yielding single-mode, diffraction-

limited operation with little or no loss in efficiency. By effectively

decoupling core diameter from beam quality, the mode-

filtering technique breaks the single-mode power limit on fiber

lasers and amplifiers without sacrificing the other key

advantages of fiber sources. At the time of its invention in 2000

and patent issuance in 2002, the Sandia/NRL approach

shattered conventional wisdom, which held that multimode

fibers could not produce high beam quality or, at best, were

extremely sensitive to handling and bending.

The principle of operation of a Mode-Filtered Fiber Amplifier is

shown qualitatively in Figure 2 and quantitatively in Figure 3.

Sandia/NRL’s coiling technique takes advantage of the fact that

the desired fundamental mode is the least sensitive to bend

loss (Figure 3); by strategically choosing the radius of curvature

(spool diameter), it is possible to introduce very high loss for

all high-order modes but negligible loss for the fundamental

mode – thus filtering out the high-order modes and extracting

all the light energy in the fundamental mode only. By suppressing

propagation of high-order modes along the entire length of

the fiber amplifier, the energy in the gain medium is left to be

extracted in the desired fundamental mode. Thus high-power,

single-mode operation is obtained without compromising any

other performance characteristics.

Figure 2: Illustration of the mode-filtering technique. In an appropriately coiled multimode fiber amplifier the undesired high-order modes are radiated from the side of the fiber along its entire length, whereas the desired fundamental mode is transmitted without significant attenuation. This “distributed spatial filtering” is accomplished by select-ing a bend radius that permits propagation of the fundamental mode but introduces substantial bend loss for high-order modes. The figure is not drawn to scale. Typical diameters are ~0.25 mm for the fiber and ~50 mm for the coil, and the typical fiber length is ~5 m.



�0

The net result is shown in Figure 4, which displays photographs

of the output face of a fiber amplifier when operated

conventionally and when it is mode filtered using the Sandia/

NRL technique; the dramatic improvement in beam quality is

evident.

Recognition of the Significance of the Sandia/NRL Advance

The significance of mode filtering was widely recognized in

the laser field and even in the broader scientific community.

Following publication in the premiere journal Optics Letters, the

invention was extensively covered in the leading laser and

optics trade journals (including Laser Focus World and Photonics

Online) and was selected as an “example of the most significant

recent research in optics and engineering,” and one of “the

‘hottest’ topics in current optics research” by the Optical Society

of America (Optics and Photonics News). It was also highlighted

in the “Editor’s Choice” column of the prestigious journal Science.

More importantly, the technique was adopted by R&D groups

worldwide. Breaking the single-mode power limit (along with

the availability of more powerful pump diode sources) led to

dramatic increases in attainable power from fiber lasers

(Figure 5) – a trend that continues today.

Figure �: Experimental comparison of the output beam from a fiber amplifier that is not mode filtered (left) vs. mode-filtered (right). The fiber supports 24 modes, and the core is denoted by the circles in the lower panels (25 micron diameter). The conventional unfiltered fiber amplifier produces a beam that is highly multimode, exhibiting unde-sirable structure and “hot spots” that vary with opti-cal power level, vibration, time, handling of the fiber, etc., as the fiber modes compete for the optical gain; the beam is also highly divergent. In contrast, the mode-filtered beam is unstructured and stable, with diffraction-limited beam quality.


Figure 3: Calculation showing the principle of operation for mode filtering. The graph plots the transmittance of some of the modes of a multimode fiber as a function of spool diameter. The fiber supports 14 modes, but only the low-est four modes are plotted. The spatial pattern of each mode is shown, with the circle denoting the fiber core (30 micron diameter). The desired fundamental mode (LP

01) is the least sensitive to

bend loss. As indicated by the yellow bar, coiling the fiber on a spool with a diameter of 10-12 cm will provide high loss (low transmittance) for all undesired high-order modes while allowing the fundamental mode to be transmitted with very little attenuation. Note that the fundamental mode has a Gaussian spatial profile, providing diffraction-limited beam quality; the high-order modes have more structured profiles and are not diffraction-limited.


��

Figure �: Output power of diffraction-limited fiber lasers as a function of time. (Source: Nufern)


CW Fiber Lasers: diffraction-limited, single-fiber results


��

As explained earlier under “Product Price,” the Mode-Filtered

Fiber Amplifier technology is licensed to users rather than

manufactured by Sandia/NRL, and products competitive with

the fibers, components, lasers, and laser systems that use it

are broad and varied. Nevertheless, we provide a competitive

comparison of mode-filtered fiber lasers vs. conventional laser

systems in the next section.

Product’s Competitors


��

Comparison Matrix We first provide a general comparison of the performance

characteristics of fiber lasers with competing laser technologies.

We then compare the specifications of a commercial mode-

filtered fiber laser with two commercial solid-state lasers in

order to quantitatively illustrate the benefits of the Sandia/NRL

invention.

Recently, manufacturers have prepared a number of

comparisons of the performance of fiber lasers vs. high-power

lasers traditionally used in materials processing (the laser

application with the largest market share). Information that

appeared in Industrial Laser Solutions (February 2006)

summarizes the main attributes and illustrates the commanding

lead now held by fiber lasers (Figure 6).

Discussion of Advantages

Power & Footprint: As discrete lower-power units are

coupled together, it is now possible to deliver >30 kiloWatts

(kW) of optical power from a fiber laser, rivaling the output of

traditional solid-state units. Owing to more compact packaging

and lower cooling requirements, however, fiber lasers range

from 3x smaller than disk lasers (their nearest competitor) to

>20x smaller than Nd:YAG sources (the dominant solid-state

laser technology); the advantage over gas lasers (e.g., CO2) is

Figure �: Comparison of laser system attributes. (Source: High-power fiber lasers gain market share, Industrial Laser Solutions, February 2006, reprinted with permission.)


��

even greater. A multi-kW fiber laser system can reduce floor

space requirements (footprint) from 10 square meters to less

than 1.5 square meters.

Beam Quality: The fundamental design of mode-filtered fiber

lasers provides diffraction-limited beam quality (Figure 4),

which does not degrade as power levels increase. The beam

divergence of a fiber laser is one-tenth that of a CO2 laser with a

similar spot size, and it is significantly less than that of competing

solid-state sources, even at power levels of <1 kW.

Wavelength Flexibility: The broad gain bandwidth of

Yb-doped fiber allows lasing anywhere from 1000 to 1200 nm,

and depending on the dopant used, fiber lasers can provide

coverage across the spectrum from 1000 to 2000 nm.

Furthermore, the infrared output of fiber lasers

can be efficiently frequency-converted to

other wavelengths, such as the ultraviolet (UV).

Maintenance & Operating Costs: Because there are no external optics to replace

or align, and cooling requirements are minimal,

fiber lasers require significantly less

maintenance than conventional lasers. Now

that high-power fiber-laser products have

broken into manufacturing environments and

have generated sufficient operating

history for realistic comparisons to be made, it has been shown

that operating costs are roughly a factor of two less than CO2

lasers and nearly a factor of four less than other solid-state

systems (Figure 7).

Figure 7: Comparison of operating costs for 4 kW lasers.(Source: “High-power fiber lasers gain market share,” Industrial Laser Solutions, February 2006, reprinted with permission.)

Comparison Matrix


��

Specific comparisons of a Nufern mode-filtered fiber laser to

traditional solid-state lasers are given in Figure 8 and discussed

below.

Mode-Filtered Fiber Laser

Nd:YAG Laser Nd:YVO� Laser

Manufacturer Nufern Spectron EdgeWave

Output power (W) 180 40 200

Beam quality (M2) < 1.1 < 1.3 < 2

Operating mode continuous wave continuous wave continuous wave

Pump source diode lasers diode lasers diode lasers

Electrical power (W) 640 1000 1500

Electrical efficiency 28% 4% 13%

Volume, including power supply (cm3)

6750 44,700 193,000 including chiller

Figure 8: Comparison of a commercial mode-filtered fiber laser vs. two commercial solid-state lasers.

Comparison Matrix


��

For the purpose of this application, this section might be more

appropriately labeled “How our invention improves on

competitive products or technologies” because the Mode-

Filtered Fiber Amplifier opened the door to a wide range of

high-power fiber-laser products, allowing them to compete

with numerous traditional solid-state laser systems. Fibers

designed for mode filtering and licensed products incorporating

mode-filtered fiber amplifiers form the basis of the business

plan and product roadmap of co-applicants Nufern and Liekki,

and three other companies recently signed licenses for the patent.

Figure 8 compares some of the key specifications of three

commercial products: a mode-filtered fiber laser, a Nd:YAG

laser, and a Nd:YVO4 laser. The most important specifications of

a laser system are application dependent, and a large number

of optical and physical specifications are required to completely

characterize the system. Furthermore, mode-filtered fiber

amplifiers are incorporated into a wide range of products

(continuous wave and pulsed, various power levels, various

wavelengths, etc.). Any comparison thus provides only a

“snapshot” of the technologies, but the data given in Figure 8

are representative and clearly illustrate the advantages of the

mode-filtered fiber laser over previous solid-state laser

technologies. Following a detailed comparison of these

products in the two paragraphs below, we discuss the

advantages of mode-filtered fiber lasers more generally.

As illustrated in Figure 8, the Nufern mode-filtered fiber laser

delivers high power and simultaneously high beam quality

(expressed here as the value M2, where M2 = 1.0 denotes the

diffraction limit). The Spectron Nd:YAG laser was chosen for

comparison because it provides near-diffraction-limited beam

quality, although its power level is significantly lower (40 W vs.

180 W). Despite having nearly a factor of five higher output

power, the mode-filtered fiber laser has a volume that is

approximately one-sixth that of the Nd:YAG laser (i.e., the

volume per Watt of output power is a factor of 30 better for the

How Our Product Improves upon Competitive Products or Technologies


��

mode-filtered fiber laser). Furthermore, the electrical efficiency

of the mode-filtered fiber laser is dramatically higher – a factor

of 7 improvement. Stated differently, despite consuming 1.6x

the electrical power of the mode-filtered fiber laser, the Nd:YAG

laser produces only 22% of the output power.

The Nd:YVO4 laser was chosen for comparison because its output

power is comparable to that of the mode-filtered fiber laser

(although it does not achieve diffraction-limited beam quality)

and because this bulk crystalline gain medium represents the

latest advance in efficiency among diode-pumped solid-state

lasers. Although the efficiency of the Nd:YVO4 laser is 3x that of

the Nd:YAG laser, the mode-filtered fiber laser is still a factor of

2 more efficient; furthermore the beam quality of the fiber laser

is better by a factor of 2 at a comparable power level. (An exact

comparison of size could not be given here because the power

supply in the Nd:YVO4 laser is integrated with the chiller.

However, the laser head without the power supply is already

twice as large as the mode-filtered fiber laser including the

power supply, still highlighting the inherent advantage of the

mode-filtered fiber laser.)

Compared to Nd:YAG lasers (the dominant solid-state laser

source), specific benefits of mode-filtered fiber-laser

technology include:

• A 5-fold increase in wall-plug efficiency (from typically

<5% to ~25%).

• Elimination of external cooling – further reducing cost

and bulk and increasing reliability.

• Stable, diffraction-limited beam quality that is insensitive

to external perturbations or optical power level –

allowing delivery of laser power with the smallest

possible spot size.

• Ability to incorporate optical components

monolithically into the fiber, thereby replacing free-

space optics, eliminating alignment problems and

increasing system ruggedness and reliability.



��

• Continuous tunability and wavelength agility for

targeting specific molecules or absorption features.

Each of these benefits is discussed below.

High Electrical Efficiency

Simply stated, fiber lasers operate much more efficiently than

conventional gas or solid-state lasers. The inherent efficiency

of the fiber laser is unrivalled when compared to existing laser

technologies (see Figure 9).

Low Waste Heat Generation

Figure 10 shows the energy levels associated with pumping

and lasing in Nd:YAG and Yb-doped fiber lasers,

illustrating that the “quantum defect” (difference between

pump and emission energy) is smaller for the Yb-doped fiber

laser so less heat is generated. Because less heat is generated

per pump photon in a fiber laser, the lasing efficiency is

correspondingly higher. In the example shown in Figure 10, the

waste heat is reduced by a factor of 2.4 (from 24% to 10%).

Laser Optical-Optical Efficiency Electrical Efficiency *Lamp-pumped Nd:YAG 4 % 1 %

Diode-pumped Nd:YAG 40 % 16 %

Yb:YAG Disk 40 % 16 %

CO2

N/A 10 %

Yb-doped fiber 75 % 30 %

* Electical efficiency = optical-optical efficiency x diode efficiency.

Figure 9: Laser efficiency by type. The electrical efficiencies given in the table do not include the power requirements of the cooling system, which can be significant (e.g., the wall-plug efficiency of a diode-pumped Nd:YAG laser is typically <5%). (Source: Nufern)


Figure 10: Illustration of quantum efficiency. (Source: Nufern)


��

Low Loss from the Gain Medium

With fiber lasers the pump absorption is distributed over the

entire fiber length, and the pump light is never lost because it

is confined and guided by total internal reflection in the fiber,

with virtually no attenuation. In a typical solid-state laser, the

pump and signal beams propagate and diffract freely rather

than being confined to the gain medium. As a result, the gain

that can be extracted from the system is relatively low (~101),

and the net wall-plug efficiency (amount of electrical

input energy that is ultimately converted to output light) is

typically less than 5%. The vast majority of the input energy is

thus not converted to light, but rather is wasted as heat energy

that must be removed. In fiber lasers, the fiber gain medium

acts as a “light pipe” that confines the pump and signal beams,

effectively allowing more pump energy to be captured and

converted. This unique feature of fiber lasers results in much

higher gain (~104 – 105) and dramatically higher efficiency – as

high as 40% wall-plug efficiency in laboratory systems

demonstrated by Sandia/NRL researchers.

Stable Diffraction-Limited Beam Quality

The next important fundamental fiber property to consider is

the ability of single-mode fibers to support only the

fundamental mode (LP01

), resulting in a stable, diffraction-

limited beam (see explanation presented earlier under

“Product’s Primary Function,” especially Figure 4). In contrast,

the free-space cavity design of a conventional laser system

makes it difficult to achieve diffraction-limited beam quality – the

beam quality is sensitive to alignment, vibration, temperature

shifts, and optical power level, which contributes to unstable

beam quality and variations in optical power. In essence, the

beam quality of a fiber laser is engineered into the gain

medium, whereas that of a conventional laser system is subject

to the influence of a multitude of environmental and

operational variables. Figure 4 shows a comparison of a single-

mode, diffraction-limited beam and a multimode beam.



�0

Facile Thermal Management

Another distinguishing feature of optical fibers is their high

surface-area-to-volume ratio, resulting in facile heat removal

— allowing fiber lasers to be air-cooled. In addition to efficiently

confining light and producing desirable beam quality, optical

fibers have a high surface-area-to-volume ratio, resulting in

facile heat removal – allowing fiber lasers to be air-cooled. By

contrast, the bulk gain media (e.g., Nd:YAG rods or Yb:YAG disks)

employed in typical solid-state laser systems have relatively

little surface area, making heat removal difficult, as illustrated

in Figure 11.

Solid-state laser systems using bulk crystalline gain media must

generally be intensively water-cooled, adding to system bulk,

complexity, instability, and cost of operation. It should be noted

that the fundamental inefficiency of conventional laser systems

is greatly reinforced by the heat-removal problem – not only

does a bulk medium produce far more heat than a fiber, but it

is also significantly more difficult to remove that heat. Further-

more, thermal effects in the bulk gain medium can substantially

degrade the beam quality, exacerbating the problems of these

technologies.

Figure 11: Fiber Laser Thermal Management. (Source: Nufern)



��

Monolithic System Architecture

Another attractive design feature of fibers is the ability to

monolithically incorporate optical components directly into the

fiber (such as lenses, mirrors, and gratings). This capability

enables a hermetically sealed, alignment-free optical path,

thereby increasing system reliability and ruggedness. By

contrast, non-fiber systems direct a free-space beam through

discrete optical components, which are subject to misalign-

ment, contamination, and damage. Figure 12 illustrates how

optical elements can be incorporated into the fiber to create a

laser cavity (rather than the “master oscillator – power

amplifier” configuration depicted in Figure 1a). Note also that

the fiber is coiled at a strategically chosen diameter to effect

mode filtering, as described earlier.

Broad Wavelength Coverage

Finally, gain media based on crystalline materials (e.g., YAG, YLF,

YVO4, etc.) are characterized by sharp optical transitions, which

result in an output of discrete operating wavelengths. Rare-

earth-doped fibers exhibit broad optical transitions, which

result in a wide range of operating wavelengths and continu-

ous tunability. The advantage of this wavelength agility and

tunability is that the laser system can produce a range of

desired wavelengths on demand, which is useful in a number of

applications discussed below.

Figure 12: High-power, mode- filtered fiber laser with optics embedded monolithically into the fiber.



��

Prior to 2002, the initial application of fiber lasers occurred in

the telecommunications sector, where the primary advantage

was that laser light could be amplified within an optical fiber.

Traditionally, optical signals propagating in a fiber had to be

removed from the fiber, converted to an electrical signal, amplified,

converted back into an optical signal, and then re-injected into

the communications fiber – an extremely cumbersome and

inefficient process that had to be repeated at regular

intervals as transmission degraded over distance. These

traditional “repeaters” were replaced by “optical repeaters”

based on fiber amplifiers, which directly amplify the optical

signal in the fiber, thereby eliminating the electrical-optical

conversion steps, electrical amplification, and re-injection of the

amplified signal. This advance enabled the optical

telecommunications revolution. Telecommunications provided

the proving ground for fiber lasers, allowing the technology to

demonstrate its practical advantages, to mature, and then to

achieve the explosive growth that is the hallmark of a

game-changing technology.

As noted earlier under “Product’s Primary Function”, fiber lasers

were limited to low-power applications until the invention of

the Mode-Filtered Fiber Amplifier by Sandia/NRL broke this

barrier, providing the technology with entry into mainstream

applications. Foremost among these is materials processing,

where fiber lasers have already begun to capture a significant

share of this >$1.7B market. Overall fiber laser sales exhibited a

growth rate of 55 percent between 2005 and 2006 (to >$199M).

(Source: “LASER MARKETPLACE 2007: Laser industry navigates

its way back to profitability,” Laser Focus World, January 2007.)

The workhorse of the solid-state commercial materials

processing market is the Nd:YAG laser, operating at a

wavelength of 1064 nm. Yb-doped fiber lasers currently

offer a direct replacement at this wavelength. Fiber lasers have

penetrated materials processing applications so quickly that it

is expected that sales in this segment will comprise >$187M in

Principal Applications


��

2007, nearly 75% of all sales of fiber lasers. The dominant

applications within materials processing are marking, cutting,

cladding, drilling, and welding. Of these, the lowest-power

application is laser marking, where fiber lasers already

comprise >20% of the market and are displacing Nd:YAG units

at an astonishing rate. Similar gains are expected in the remaining

applications as available power levels continue to increase.

Beyond these entry-level uses (where fiber lasers replace

existing devices), continued development of pulsed fiber lasers

– which deliver very short, intense bursts of light rather than

a continuous stream of energy – is expected to open up more

advanced application areas, such as semiconductor processing,

high-aspect-ratio drilling, and processing of refractory

materials. Note that the Sandia/NRL mode-filtering technique

is equally enabling for both pulsed and continuous-wave fiber

lasers, and the first two Sandia/NRL publications on the

technology (Appendix B) demonstrated both modes of

operation.

Principal Applications


��

Owing to the wavelength agility cited earlier, fiber lasers are

not limited to a few fundamental wavelengths. Sandia/NRL’s

mode-filtering technique has recently enabled generation of

high peak powers (in excess of 1000 kW), which provide

efficient conversion to other wavelengths – the ultraviolet (UV)

region is of particular interest. The ability to deliver >10 Watts

of UV power opens up applications in the electronics industry,

especially semiconductor processing for manufacturing memory

and computer chips (e.g., “link blowing” for maximizing yield in

the production of semiconductor wafers), via drilling in circuit

boards, electronics prototyping via subtractive board

fabrication, and photolithography.

Compact, reliable laser sources are also in demand in the field

of sensing – applications include:

• ranging and altimetry;

• three-dimensional mapping using laser radar (ladar);

• remote physical sensing, such as light detection and

ranging (lidar);

• real-time, in situ and remote detection of chemical and

biological compounds, (e.g., for pollution detection

and prevention, and for process control in the energy

and semiconductor industries); and

• medical diagnostics (e.g., breath analysis).

Other Applications


��

Despite great advances in spectral coverage and output power,

high-power lasers remained predominantly laboratory tools

that were bulky, fragile, inefficient, and/or provided poor beam

quality. Massive investments (billions of dollars) in various laser

technologies failed to overcome these limitations, and numerous

potential applications of lasers were thus rendered impractical.

Fiber lasers offered the possibility to unlock the full technological

potential inherent in lasers and laser-based instruments, but

fundamental limitations constrained this technology to low

output powers and pulse energies. Sandia/NRL’s Mode-Filtered

Fiber Amplifier solved this long-standing problem, finally

unlocking the full potential of fiber lasers.

Sandia/NRL’s Mode-Filtered Fiber Amplifier technology

represents a breakthrough that enables miniature, ultra-

efficient, high-power laser sources that are revolutionizing the

application of lasers to real-world problems. The Mode-Filtered

Fiber Amplifier is an enabling technology that is elegantly

simple but that shattered conventional wisdom by effectively

decoupling fiber core size (power-generating capability) from

beam quality.

Prior to its invention, operating a highly multimode fiber

laser efficiently and stably on a single mode was considered

a contradiction in terms. The solution – strategically coiling a

fiber – is simple, contributes to compact packaging, and does

not increase either the cost or the complexity of the laser

system. It is this practical simplicity that makes the technology

such a game-changer in so many application areas, and thus

has led to the explosive growth described in this R&D 100

Award application.

The Sandia/NRL mode-filtering technique has been adopted

by both academic and industrial R&D groups worldwide to

achieve record-setting power levels from diffraction-limited

fiber sources, and it has become the de facto standard for

power scaling of pulsed and continuous-wave fiber lasers and

Summary


��

amplifiers. The technology has been licensed and

commercialized by five companies in the U.S. and other

countries. The invention is universally applicable across many

fiber types and touches virtually every application area where

lasers may be used.

Summary


��

Contact Person to Handle All Arrangements on Exhibits,

Banquets, and Publicity

Robert W. Carling

Director

Sandia National Laboratories

P.O. Box 969, Mail Stop 9405

Livermore, CA 94551-0969, USA

925-294-2206 (phone)

925-294-3403 (fax)

[email protected]


��

Appendix A: Front-Page Patent Image


��

Appendix B: Front-Page Papers and Articles

Key papers and articles are listed below. A front-page image from each source is supplied on the pages fol-

lowing the list.

Selected archival papers written by the team: • “Single-mode operation of a coiled multimode fiber amplifier,” Koplow, JP; Kliner, DAV;

Goldberg, L; in Optics Letters; April 1, 2000; v.25, no.7, p.442-444.

• “Diffraction-limited, �00-kW peak-power pulses from a coiled multimode fiber amplifier,”

Di Teodoro, F; Koplow, JP; Moore, SW; Kliner, DAV; in Optics Letters; April 1, 2002; v.27, no.7, p.518-520.

• “High-Peak-Power (>�.� MW) Pulsed Fiber Amplifier,” Farrow, RL; Kliner, DAV; Schrader, P.E.;

Hoops, AA; Moore, SW; Hadley, G R and Schmitt, RL; Proc. SPIE Vol. 6102,61020L, Fiber Lasers III:

Technology, Systems, and Applications; February 2006.

Technical articles written by the team: • “Single-transverse-mode operation of a coiled multimode fiber amplifier,” Koplow, JP; Kliner,

DAV; Goldberg, L; in Optics and Photonics News; December 2000; v.11, no.12, p.21-22.

• “Fiber Laser Technology Reels in High Power Results,” Kliner, DAV Koplow, JP and Di Teodoro, F;

oe magazine, January 2004. [Available at http://oemagazine.com/fromthemagazine/jan04/tutorial.

html ]

Articles recognizing the invention of the Mode-Filtered Fiber Amplifier: • ”Optics in �000,” Optics and Photonics News, issue 11, no 12, p. 16, December 2000.

• “CLEO �000: Coiled fiber amplifiers produce high power single-mode pulses,”

Yvonne Carts-Powell, Photonics Online, May 12, 2000. [Available at http://www.photonicsonline.com/

content/news/article.asp?docid={988b6850-275d-11d4-8c3c-009027de0829} ]

• “FIBER AMPLIFIERS: Coiling boosts single-mode power in multimode fiber,” Hassaun Jones-Bey,

Laser Focus World, August 2000. [Available at http://lfw.pennnet.com/articles/article_display.cfm?

Section=ARCHI&C=News&ARTICLE_ID=79975&KEYWORDS=koplow&p=12 ]

• “Coiled fiber amplifier delivers high-power signal,” Hassaun A. Jones-Bey, Laser Focus World, June

2002. [Available at http://lfw.pennnet.com/articles/article_display.cfm?Section=ARCHI&C=OptWr&

ARTICLE_ID=145099&KEYWORDS=koplow&p=12 ]

• “APPLIED PHYSICS: Powering Up in Single Mode,” Ian S. Osborne, et al., Editor’s Choice section in

Science 296, 17b, April 5, 2002.


�0


Other references: • “LASER MARKETPLACE �00�: Laser industry navigates its way back to profitability,” Kathy Kincade

and Stephen Anderson, Laser Focus World, January 2007. [Available at http://lfw.pennnet.com/dis-

play_article/282527/12/ARTCL/none/none/LASER-MARKETPLACE-2007:-Laser-industry-navigates-

its-way-back-to-profitability/ ]

• “Fiber Laser Technology Review,” a webcast presentation by Andrew Held of Nufern, May 17, 2006.

[This webcast – audio and slides -- may be accessed from http://www.smalltimes.com/webcast/dis-

play_webcast.cfm?id=200 ]


��


“Single-mode operation of a coiled multimode fiber amplifier,” Optics Letters; April 1 2000; v.25,

no.7, p.442-444.


��


“Diffraction-limited, �00-kW peak-power pulses from a coiled multimode fiber amplifier,” Optics Letters; April 1 2002; v.27, no.7, p.518-520.


��


“High-Peak-Power (>�.� MW) Pulsed Fiber Amplifier,” Proc. SPIE Vol. 6102, 61020L, Fiber Lasers III:

Technology, Systems, and Applications; February 2006.


��


“Single-transverse-mode operation of a coiled multimode fiber amplifier,” Optics and Photonics News;

December 2000; v.11, no.12, p.21-22.


��


“Single-transverse-mode operation of a coiled multimode fiber amplifier,” Optics and Photonics News;

December 2000; v.11, no.12, p.21-22.


��


“Fiber Laser Technology Reels in High Power Results,” oe magazine, January 2004.


��


”Optics in �000,” Optics and Photonics News, issue 11, no 12, p. 16, December 2000.


��


“CLEO �000: Coiled fiber amplifiers produce high power single-mode pulses,” Photonics Online,

May 12, 2000.


��


“FIBER AMPLIFIERS: Coiling boosts single-mode power in multimode fiber,” Hassaun Jones-Bey,

Laser Focus World, August 2000.


�0


“Coiled fiber amplifier delivers high-power signal,” Hassaun A. Jones-Bey, Laser Focus World, June 2002.


��


“APPLIED PHYSICS: Powering Up in Single Mode,” Editor’s Choice section in Science 296, 17b, April 5, 2002


��


“LASER MARKETPLACE �00�: Laser industry navigates its way back to profitability,” Laser Focus World,

January 2007.


��


“Fiber Laser Technology Review,” a webcast presentation by Andrew Held of Nufern, May 17, 2006.

Documents

2007 R&D 100 Award Entry Form Mode-Filtered Fiber Amplifier · 2020. 9. 4. · 2007 R&D 100 Award Entry Form Mode-Filtered Fiber Amplifier Dahv A.V. Kliner Distinguished Member of